Pneumatic brake actuator with flow insensitive two way control valve

ABSTRACT

A pneumatic brake actuator has a spring brake actuator with spring and spring brake pressure chambers, and a service brake actuator with service brake pressure and pushrod chambers. A control valve has a seal that is moveable between an open position and a closed position for regulating fluid flow between the spring chamber and service brake pressure chamber. A first surface of the seal is in fluid communication with the service brake pressure chamber and a second surface of the seal is in fluid communication with a valve chamber that is not in fluid communication with the service brake pressure chamber or spring chamber. The seal moves between its open and closed positions based on a pressure in the service brake pressure chamber. Movement of the seal is not dependent on the rate of flow of fluid between the spring chamber and the service brake pressure chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application clams priority to and is a Continuation of U.S. patentapplication Ser. No. 13/465,126, filed on May 7, 2012 and issued on Mar.17, 2015 as U.S. Pat. No. 8,978,839, and of U.S. patent application Ser.No. 14/614,804 filed on Feb. 5, 2015, which are incorporated herein byreference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to pneumatic brakeactuators, and more specifically to a pneumatic brake actuator with atwo-way control valve.

2. Description of Related Art

A pneumatic brake system for a large, heavy-duty vehicle such as a bus,truck, semi-tractor, or trailer typically includes a brake shoe and drumassembly which is actuated by an actuator that is operated by theselective application of compressed air. Conventional pneumatic springbrake actuators have both a service brake actuator for actuating thebrakes under normal driving conditions by the application of compressedair and a spring-type emergency brake actuator which actuates the brakeswhen air pressure has been released from a pressure chamber. Theemergency brake actuator, or spring brake, includes a strong compressionspring which applies the brake when air is released.

There are two main types of pneumatic brake actuators, piston typeactuators and diaphragm type actuators. In the diaphragm type brakeactuator, two pneumatic diaphragm brake actuators are typically arrangedin a tandem configuration, which includes a pneumatic service brakeactuator for applying the normal operating brakes of the vehicle, and aspring brake actuator for applying the parking or emergency brakes ofthe vehicle. Both the service brake actuator and the spring brakeactuator include a housing having an elastomeric diaphragm dividing theinterior of the housing into two distinct fluid chambers. The pistontype brake actuator is substantially similar to the diaphragm type,except that instead of a diaphragm, a piston reciprocates in a cylinderfor applying the normal and/or parking brakes of the vehicle.

In a typical service brake actuator, the service brake housing isdivided into a pressure chamber and a pushrod chamber. The pressurechamber is fluidly connected to a source of pressurized air and thepushrod chamber mounts a pushrod that is coupled to the brake assembly.The introduction and exhaustion of pressurized air in to and out of thepressurized chamber reciprocates the pushrod in to and out of thehousing to apply and release the operating brakes.

In a typical spring brake actuator, the spring brake section is dividedinto a pressure chamber and a spring chamber by a diaphragm. A pressureplate is positioned in the spring chamber between the diaphragm and astrong compression spring, whose opposing end abuts the housing of thesection. In one well-known configuration, an actuator tube extendsthrough the pressure plate, through the diaphragm, into the pressurechamber, and through a dividing wall separating the spring brakeactuator from the service brake actuator. The end of the actuator tubeis fluidly connected to the pressure chamber of the service brakeactuator.

When applying the parking brakes, the spring brake actuator pressure isdischarged from the pressure chamber and the large force compressionspring pushes the pressure plate and the diaphragm toward the dividingwall between the spring brake actuator and the service brake actuator.In this position, the actuator tube connected to the pressure plate ispushed for applying the parking or emergency brakes and thusimmobilizing the vehicle. To release the parking brake, pressurized airis introduced into the pressure chamber of the spring brake actuator toexpand the pressure chamber, move the diaphragm and pressure platetoward the opposing end of the spring brake actuator housing, andcompress the compression spring.

One known problem in association with spring brake actuators of thisdesign is that as the large force compression spring is compressed, thepressure chamber increases in volume and the spring chamber decreases involume, resulting in a pressure increase in the spring chamber. Thebuild-up of pressure in the spring chamber upon the release of the brakeis highly undesirable in that any pressure build-up in the springchamber must be offset by an increased pressure in the pressure chamberin order to fully compress the spring and thus fully release the brake.

The undesirable effects of pressure build-up in the spring chamber areexacerbated due to the fact that most pressurized air systems forheavy-duty vehicles operate at an industry standard maximum pressure. Ifthe combined pressure of the spring and the air pressure in the springchamber approach that maximum pressure then the emergency brake can failto release, only partially release, or release very slowly, all of whichare undesirable.

One solution to prevent pressure increase in the spring chamber is toinclude vent holes in the spring chamber housing. These vent holes areundesirable because they expose the interior of the spring chamber toexternal environmental elements such as dirt, salt, and water, whichaccelerate abrasion, corrosion, or wear on the various internal brakecomponents such as the spring. The damage to the internal brakecomponents by environmental elements can require increased maintenanceor cause premature failure of the spring. To prevent environmentalelements from entering the spring brake housing, it is known to place afilter over the vent openings. The filtered vent openings, however,inherently permit external air to enter the brake, yielding a brake thatis not completely sealed. Additionally, the filters require increasedmaintenance because they must be cleaned and/or replaced and typicallydo not effectively prevent water from entering the spring chamber.

An additional problem with directly externally venting the springchamber is that the types of vehicles on which the actuator is mounted,such as tractor trailers, are often parked for extended periods in adock bay. The bays are typically sloped and below grade, and under heavyrain or snow conditions can fill with water to a height that floods theinterior of the actuator's spring chamber. Although the water isnormally expelled from the spring chamber through the vent openings asthe brake is released, the flooding can accelerate corrosion andintroduce other environmental hazards. Further, if it is below freezing,the water can freeze and prevent release of the brake. Filtered ventopenings do not prevent water from flooding the spring chamber.

In order to eliminate the pressure build-up in the spring chamber whilekeeping out environmental elements, it is known to include a fluid flowpath between the spring chamber of the spring brake actuator and theservice brake pressure chamber through the actuator tube. In such anactuator, a control valve is placed in the actuator tube to regulate airflow between the spring chamber and service brake pressure chamber. Twotypes of control valves have been used, two-way control valves andone-way control valves.

One-way control valves allow air to flow from the spring chamber intothe service brake pressure chamber to prevent pressure build up in thespring chamber when the volume of the spring chamber decreases. However,when the spring brake is applied and the volume of the spring chamberincreases, the one-way valve remains in its closed position and does notallow air to flow from the service brake pressure chamber into theexpanding spring chamber. This causes a vacuum to form in the springchamber such that volume enclosed by the spring chamber is at a negativerelative pressure, which reduces the load provided by the parkingbrakes. In order to overcome the vacuum formation in the spring chamber,it is necessary to use a larger spring in the spring chamber that iscapable of overcoming the negative relative pressure caused by thevacuum. While pneumatic brake actuators with one-way control valvestypically allow air to enter the spring chamber through the opening thatthe caging bolt passes through when the spring is caged, this opening issealed during normal operation of the actuator.

Two-way control valves allow air to vent from the spring chamber whenthe spring is compressed and they allow air to enter the spring chamberwhen the spring brake is applied. Conventional two-way control valves,however, are flow rate sensitive, which means that they will only closedue to increased pressure in the service brake pressure chamber if theflow of fluid into the service brake pressure chamber and through thevalve reaches a certain level. If fluid slowly moves through the valvewhile the service brake pressure chamber increases, the valve remainsopen, thereby allowing the pressure to increase in both the servicebrake pressure chamber and the spring chamber. This results inapplication of both the service brake and the spring brake whichsubjects the brake system's components to increased levels of force thatmay cause damage.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention is directed toward a pneumaticbrake actuator having a spring brake actuator coupled with a servicebrake actuator. The spring brake actuator has a spring chamber and aspring brake pressure chamber, and the service brake actuator has aservice brake pressure chamber and a pushrod chamber. A control valve isoperable to regulate fluid flow between the spring chamber and theservice brake pressure chamber. The control valve includes a seal thatis moveable between an open position, in which fluid can flow betweenthe spring chamber and the service brake pressure chamber, and a closedposition, in which fluid is blocked from flowing between the springchamber and the service brake pressure chamber. The seal has a firstsurface in fluid communication with the service brake pressure chamberand a second surface in fluid communication with a valve chamber that isnot in fluid communication with the service brake pressure chamber orthe spring chamber. The seal moves between the open position and theclosed position based on a pressure in the service brake pressurechamber.

Preferably, the pressure in the service brake pressure chamber is afirst pressure and a pressure in the valve chamber is a second pressure.A first force is exerted on the first surface due to the first pressureacting on the first surface, and a second force is exerted on the secondsurface due to the second pressure acting on the second surface. Theseal moves from its open position to its closed position when the firstforce is greater than the second force. A spring may exert a third forceon the second surface, in which case the seal moves from its openposition to its closed position when the first force is greater than thesum of the second and third forces.

Preferably, movement of the seal is not dependent on the rate of flow offluid or pressure differential between the spring chamber and theservice brake pressure chamber. The control valve is preferably a pilotoperated valve where the pilot pressure is the pressure in the servicebrake pressure chamber. Preferably, the control valve includes a valvebody and the seal is placed within a channel formed in the valve body.When the seal is in its open position, fluid can flow through thechannel between the service brake pressure chamber and spring chamber,and when the seal is in its closed position, the channel is blocked.Preferably, the valve chamber is enclosed by the seal and the valvebody. The valve chamber may also be vented to the atmosphere.Preferably, a spring biases the seal to its open position. However, itis within the scope of the invention for the seal to be constructed froma material and in a manner that it biases itself to its open position.Alternatively, the pressure in the valve chamber may bias the seal toits open position. The spring chamber is preferably sealed to preventdirect exposure to the atmosphere and common environmental contaminants.

Biasing the control valve to its open position allows air exchangebetween the spring chamber and the service brake pressure chamber whenthe service brake pressure chamber is not pressurized. When in its openposition, the control valve prevents pressure build-up and vacuumcreation in the spring chamber. This allows the spring brake actuator,in a sealed cavity, to be operated without the need for higher springforce to overcome vacuum formation in the spring chamber. The seal ispreferably biased to its open position with enough force to overcome anegative pressure differential between the spring chamber and valvechamber that would occur in a sealed spring chamber as the volume of thespring chamber increases during actuation of the spring brake actuator,which prevents vacuum formation in the spring chamber. The control valveseal closes when the pressure in the service brake pressure chamberreaches a threshold level to prevent pressurization of both the servicebrake pressure chamber and the spring chamber. Because movement of theseal is not dependent on the rate of flow of fluid between the servicebrake pressure chamber and spring chamber, it closes and prevents fluidfrom entering the spring chamber when the service brakes are appliedslowly.

Many embodiments of control valves are within the scope of the presentinvention. In one embodiment, the seal of the control valve includes anopening that is in fluid communication with the service brake pressurechamber and spring chamber when the seal is in its open position.Alternatively, the control valve may include a valve body with a channelthat is in fluid communication with the service brake pressure chamberand spring chamber when the seal is in its open position and that isblocked when the seal is in its closed position.

The present invention also encompasses a control valve for a pneumaticbrake actuator having a spring brake actuator and service brakeactuator. The spring brake actuator having a spring chamber and springbrake pressure chamber, and the service brake actuator having a servicebrake pressure chamber and a pushrod chamber. The control valve has avalve body with an interior surface that defines a channel between thespring chamber and the service brake pressure chamber. A seal ispositioned within the channel such that a valve chamber is enclosed bythe seal and the valve body. The seal is moveable between an openposition, in which fluid can flow through the channel between the springchamber and service brake pressure chamber, and a closed position, inwhich fluid is blocked from flowing through the channel. The sealincludes a first sealing surface that engages the valve body when theseal is in its closed position, and second and third sealing surfaceseach of which engages the valve body to seal the valve chamber from thespring chamber and the service brake pressure chamber. The seal movesbetween the open position and the closed position based on a pressure inthe service brake pressure chamber.

Preferably, the pressure in the service brake pressure chamber is afirst pressure and a pressure in the valve chamber is a second pressure.The seal has a first surface that is in fluid communication with theservice brake pressure chamber and a second surface that is in fluidcommunication with the valve chamber. A first force is exerted on thefirst surface due to the first pressure acting on the first surface, anda second force is exerted on the second surface due to the secondpressure acting on the second surface. The seal moves from its openposition to its closed position when the first force is greater than thesecond force. A spring may exert a third force on the second surface, inwhich case the seal moves from its open position to its closed positionwhen the first force is greater than the sum of the second and thirdforces. Preferably, movement of the seal is not dependent on the rate offlow of fluid or pressure differential between the spring chamber andthe service brake pressure chamber.

Additional aspects of the invention, together with the advantages andnovel features appurtenant thereto, will be set forth in part in thedescription which follows, and in part will become apparent to thoseskilled in the art upon examination of the following, or may be learnedfrom the practice of the invention. The objects and advantages of theinvention may be realized and attained by means of the instrumentalitiesand combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a pneumatic brake actuator havingspring and service brake actuators where a caging bolt is shownretracting a spring of the spring brake actuator;

FIG. 2 is a cross-sectional view of the brake actuator of FIG. 1 showingthe caging bolt in an extended position;

FIG. 3 is a cross-sectional view of the brake actuator of FIG. 1 showingthe service brake actuator applied;

FIG. 4 is a cross-sectional view of the brake actuator of FIG. 1 showingthe spring brake actuator applied;

FIG. 5A is a cross-sectional view of a control valve that controls fluidflow between a spring chamber of the spring brake actuator and apressure chamber of the service brake actuator of the brake actuator ofFIG. 1 where the control valve is shown in an open position;

FIG. 5B is a cross-sectional view of the control valve of FIG. 5Ashowing the control valve in a closed position;

FIG. 5C is an exploded perspective view of the control valve of FIG. 5A;

FIG. 5D is a perspective view of a bottom of a seal of the control valveof FIG. 5A;

FIG. 6A is a cross-sectional view of a first alternative embodiment ofcontrol valve shown in an open position;

FIG. 6B is a cross-sectional view of the control valve of FIG. 6A shownin a closed position;

FIG. 6C is an exploded perspective view of the control valve of FIG. 6A;

FIG. 7A is a cross-sectional view of a second alternative embodiment ofcontrol valve shown in an open position;

FIG. 7B is a cross-sectional view of the control valve of FIG. 7A shownin a closed position;

FIG. 7C is an exploded perspective view of the control valve of FIG. 7A;

FIG. 8A is a cross-sectional view of a third alternative embodiment ofcontrol valve shown in an open position;

FIG. 8B is a cross-sectional view of the control valve of FIG. 8A shownin a closed position;

FIG. 9A is a cross-sectional view of a fourth alternative embodiment ofcontrol valve shown in an open position;

FIG. 9B is a cross-sectional view of the control valve of FIG. 9A shownin a closed position;

FIG. 9C is an exploded perspective view of the control valve of FIG. 9A;

FIG. 10 is a cross-sectional view of a fifth alternative embodiment ofcontrol valve shown in an open position;

FIG. 11A is a cross-sectional view of a sixth alternative embodiment ofcontrol valve shown in an open position;

FIG. 11B is a cross-sectional view of the control valve of FIG. 11Ashown in a closed position;

FIG. 11C is an exploded perspective view of the control valve of FIG.11A;

FIG. 12A is a cross-sectional view of a seventh alternative embodimentof control valve shown in an open position;

FIG. 12B is a cross-sectional view of the control valve of FIG. 12Ashown in a closed position;

FIG. 12C is an exploded perspective view of the control valve of FIG.12A;

FIG. 13A is a cross-sectional view of an eighth alternative embodimentof control valve shown in an open position;

FIG. 13B is a cross-sectional view of the control valve of FIG. 13Ashown in a closed position;

FIG. 13C is an exploded perspective view of the control valve of FIG.13A;

FIG. 14A is a cross-sectional view of a ninth alternative embodiment ofcontrol valve shown in a closed position;

FIG. 14B is a cross-sectional view of the control valve of FIG. 14Ashown in an open position; and

FIG. 14C is an exploded perspective view of the control valve of FIG.14A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIGS. 1-4 show a tandem-type pneumatic brake actuator 10 comprising aservice brake actuator 12 in combination with a spring brake actuator14. The service brake actuator 12 applies and releases the service oroperating brakes of a vehicle. The spring brake actuator 14 is used toapply the emergency or parking brakes of the vehicle.

The service brake actuator 12 includes a housing 16 having first andsecond end walls 16 a and 16 b and a side wall 16 c that is joined withand extends between the end walls 16 a and 16 b. The spring brakeactuator 14 includes a sealed housing 18 having first and second endwalls 18 a and 18 b and a side wall 18 c that is joined with and extendsbetween the end walls 18 a and 18 b. The housings 16 and 18 are formedby an adapter housing 20 that is coupled with a service brake cover 22and a spring brake cover 24. The adapter housing 20 and spring brakecover 22 have mating flanges 20 a and 22 a, respectively, that areclamped together with a clamp 25 to secure the service brake cover 22 tothe adapter housing 20. The adapter housing 20 has another flange 20 bthat is clamped by a C-shaped rolled rim 24 a of spring brake cover 24to secure the spring brake cover 24 to the adapter housing 20. Theadapter housing 20 defines a common dividing wall separating the servicebrake housing 16 from the spring brake housing 18 while forming aportion of each housing 16 and 18 such that the second end walls 16 band 18 b are integral. It is within the scope of the invention for theadapter housing 20 to be replaced with discrete cover elements similarto the service brake cover 22 and the spring brake cover 24.

Movable members, which in this embodiment include elastomeric diaphragms30 and 32, span the interior of the service and spring brake housings 16and 18, respectively. Diaphragm 30 has a peripheral edge 30 a that issealingly clamped between the mating flanges 20 a and 22 a of theadapter housing 20 and service brake cover 22, respectively. Diaphragm32 has a peripheral edge 32 a that is sealingly clamped between theflange 20 b of adapter housing 20 and the rolled rim 24 a of springbrake cover 24. A piston-type brake actuator, which has a piston thatspans the interior of a cylindrical spring brake housing instead of adiaphragm, is also within the scope of the present invention.

Referring to the service brake actuator 12, the diaphragm 30 fluidlydivides the service brake actuator 12 into a pushrod chamber 36 and aservice brake pressure chamber 38. A pushrod 40 has a first end 40 athat is positioned within the pushrod chamber 36 and a second end 40 bpositioned outside of the service brake housing 16. A pressure plate 42is joined to the first end 40 a of the pushrod 40 and abuts diaphragm30. The pushrod 40 extends from its first end 40 a to its second end 40b through a bearing 44 disposed in an opening 46 in the service brakecover 22. A return spring 48 is positioned between the bearing 44 andthe pressure plate 42 to aid in biasing the pressure plate 42 andpushrod 40 toward the second end wall 16 b of the service brake housing16. Although not shown, in an S-cam brake assembly, the end 40 b of thepushrod 40 is coupled to a slack adjuster of an S-cam brake assemblywhereby the reciprocation of the pushrod 40 relative to the servicebrake housing 16 results in the application and release of the servicebrakes.

The service brake pressure chamber 38 is fluidly connected to a sourceof pressurized air through an inlet port 50. As the operator of thevehicle applies the brake pedal, pressurized air is introduced into theservice brake pressure chamber 38 through the inlet port 50 toreciprocate the pushrod 40. As the operator of the vehicle releases thebrake pedal, the pressurized air is exhausted from the service brakepressure chamber 38 through the inlet port 50. The addition ofpressurized air into the service brake pressure chamber 38 moves thediaphragm 30, pressure plate 42 and pushrod 40 away from the second endwall 16 b toward the first end wall 16 a to apply the service brakes.

Referring to the spring brake actuator 14, the diaphragm 32 fluidlydivides the spring brake housing 18 into a spring brake pressure chamber56 and spring chamber 58. The diaphragm extends from its peripheral edge32 a to an interior, radial edge 32 b that surrounds an opening 59 inthe diaphragm. The spring brake pressure chamber 56 is fluidly connectedto a source of pressurized air through a port (not shown) that issubstantially identical to port 50. Typically, the pressure chamber 56is supplied by a pressurized air system that is physically distinct fromthe pressurized air system supplying the service brake actuator 12. Thespring chamber 58 is sealed to protect the components therein fromdirect exposure to the atmosphere and common environmental contaminants.

A pressure plate 60 is positioned in the spring chamber 58 adjacent tothe diaphragm 32. A large force compression spring 62 is placed betweenthe pressure plate 60 and the spring brake cover 24. The pressure plate60 includes an axial opening 64 surrounded by an interior surface 66that includes a threaded portion 68, a non-threaded portion 70, and anactuator tube shoulder 72 between the two portions 68 and 70. An annulargroove 74 that is formed in the non-threaded portion 70 receives theinterior edge 32 b of the diaphragm 32. A retaining ring 78 secures thediaphragm 32 to the pressure plate 60. It is within the scope of theinvention for the actuator to not have retaining ring 78 such that thegroove 74 and configuration of the interior edge 32 b of the diaphragm32 secures the diaphragm 32 to the pressure plate 60. There is anopening 80 in the spring brake cover 24 that is aligned with the opening64 through pressure plate 60.

A hollow actuator tube 82 has a first end 82 a that fits within theaxial opening 64 and abuts the actuator tube shoulder 72 and a secondend 82 b which is positioned in the service brake pressure chamber 38.The actuator tube 82 has a side wall 84 with inner and outer surfaces 86and 88, respectively. The outer surface 88 includes a recessed portion90 that receives a portion of the interior edge 32 b of the diaphragm 32and the optional retaining ring 78. A portion of the outer surface 88abuts the non-threaded portion 70 of the pressure plate 60. The innersurface 86 includes a threaded portion 92 that is aligned with thethreaded portion 68 of the pressure plate 60.

An annular bearing or flange guide 94 has a threaded outer surface 96that engages the threaded portion 92 of actuator tube 82 and thethreaded portion 68 of pressure plate 60 thereby joining the bearing 94,actuator tube 82, and pressure plate 60. It is within the scope of theinvention for the bearing 94 to be bonded to the actuator tube 82 andpressure plate 60 in addition to or instead of being joined withthreads. For example, the bearing 94 can be welded to the actuator tube82 and/or pressure plate 60.

The bearing 94 has a smooth inner surface 97 surrounding an opening 99.The bearing 94 and the pressure plate 60 define therein air passage waysor clearances (not shown) to allow air flow back and forth between thespring chamber 58 and the interior space 98 enclosed by the side wall 84of the hollow actuator tube 82. Thus, spring chamber 58 is in fluidcommunication with the interior space 98 of the actuator tube 82.

The actuator tube 82 extends from its first end 82 a, which ispositioned in the spring chamber 58, through a bearing and seal assembly100 disposed within an opening 102 formed in the adapter housing 20 toits second end 82 b, which is positioned in the service brake pressurechamber 38. The bearing and seal assembly 100 are well known in the artand thus are not described in more detail herein.

A control valve 104, which is described in more detail below inconnection with FIGS. 5A-D, is joined to and closes the second end 82 bof the actuator tube 82 opposite the pressure plate 60 for regulatingfluid flow between spring chamber 58 and service brake pressure chamber38. The control valve 104 includes a valve body 106 having a transferplate 108 that is joined to a cylindrical protrusion 110. Thecylindrical protrusion 110 has a threaded side wall 112 that engagesthreads 114 on the inner surface 86 of the side wall 88 of the actuatortube 82. The protrusion 110 is at least partially positioned within theinterior space 98 of the actuator tube 82. A seal is formed between thethreaded side wall 112 of the control valve 104 and the side wall 88 ofthe actuator tube 82 to prevent fluid from flowing between the two. Sealstructure, such as an o-ring seal, may be positioned between the sidewall 112 of the control valve 104 and the side wall 88 of the actuatortube 82 to form the seal. Alternatively, or in addition to using sealstructure, such as an o-ring seal, a liquid sealant may be applied tothe threaded side wall 112 before the control valve 104 is threadedwithin the actuator tube 82. The liquid sealant would subsequentlyharden to form a seal between the control valve 104 and actuator tube82. The transfer plate 108 is preferably sized to be received within arecess 116 in the adapter housing 20.

The brake actuator 10 further comprises a caging bolt assembly 118comprising an adjustment nut 120 threaded onto and permanently affixedto one end of a caging bolt 122 which terminates at its other end in acaging bolt head 124. The caging bolt head 124 and a portion of thecaging bolt 122 extending from the head 124 are positioned within theinterior space 98 of the actuator tube 82. The caging bolt 122 extendsthrough the opening 99 of the bearing 94 and through the opening 80 inthe spring brake cover 24. The caging bolt 122 is threaded through a capor collar 128, which is riveted and permanently affixed to the springbrake cover 24 in a substantially sealed manner so that air cannot passthrough opening 80. Since the nut 120 and caging bolt head 124 aregreater in diameter than the diameter of the opening 99 in bearing 94,the caging bolt 122 couples the pressure plate 60 to the spring brakecover 24 via the connection between the bearing 94 and pressure plate 60and the connections between the caging bolt 122, collar 128, and springbrake cover 24.

The caging bolt head 124 preferably includes a bearing 130 positionedbetween opposing collars 132. The bearing 130 contacts the inner surface86 of the actuator tube 82 to prevent the collars 132 and caging bolt122 from contacting the inner surface 86 while helping to guide thereciprocal movement of the actuator tube 82 during the application andrelease of the emergency brakes. Axial slots 134 are formed in the faceof the bearing 130 to form a fluid flow path around the bearing 130 sothat the spring chamber 58 is in fluid communication with the entireinterior space 98 enclosed by the actuator tube 82.

The caging bolt assembly 118 is operable to mechanically retract andhold the large force compression spring 62 in a compressed state (asshown in FIG. 1). By engaging the adjustment nut 120 with a wrench orsocket and rotating the nut 120, it is possible to threadably withdrawthe majority of the caging bolt 122 out of the spring brake housing 24from the position shown in FIG. 4 to the position shown in FIG. 1. Asthe caging bolt 122 is withdrawn, the caging bolt head 124 contacts thebearing 94 at the upper end 82 a of the actuator tube 82 to move thebearing 94, actuator tube 82, and pressure plate 60 toward the end wall18 a of the spring brake housing 18 thereby compressing the spring 62.Caging the large force compression spring 62 in this manner, as shown inFIG. 1, is well known and is typically utilized during assembly of thebrake actuator 10 and/or for the mechanical release of the brakes in thecase of a failure or absence of the compressed air system. When thebrake actuator 10 is in active use on a moving vehicle, the caging bolt122 is moved to the position shown in FIGS. 2-3.

Referring now to FIGS. 5A-5D, the control valve 104 includes valve body106, and a seal 136, spring 138, and o-ring seal 140 positioned inside achannel 142 defined by an interior surface 144 of the valve body 106.The transfer plate 108 of the valve body 106 has upper and lowersurfaces 146 and 148 joined by a side wall 150. The cylindricalprotrusion 110 of the valve body 106 has upper and lower surfaces 152and 154 joined by threaded side wall 112. The lower surface 154 of theprotrusion 110 is joined to the upper surface 146 of the transfer plate108. The channel 142 through the valve body 106 includes an uppercylindrical section 156 that is enclosed by the side wall 112 ofprotrusion 110, a lower vertical section 158 extending through thetransfer plate 108 from upper surface 146 to lower surface 148, and alower horizontal section 160 that extends through the transfer plate 108between openings 162 and 164 in side wall 150.

The valve body 106 also includes a retainer 166 that is positionedwithin the channel 142 for retaining seal 136 within the channel 142.The retainer 166 is preferably press fit into the channel 142. Theretainer has a disk shaped upper section 168 that is supported by aledge 170 formed in the interior surface 144. Concentric rings 172 and174 that are integral with upper section 168 extend into channel 142. Aplug 176 that is centered in ring 174 is integral with upper section 168and extends into channel 142. Referring to FIG. 5C, there are threechannels 178, 180, and 182 that are formed in and extend through theretainer 166. Each channel 178, 180, and 182 is positioned between ring174 and plug 176, as best shown in FIG. 5A with respect to channel 182.The channels 178, 180, and 182 allow air to flow through the retainer166. O-ring 140 is positioned between ring 172 and the interior surface144 to form a seal and prevent air from flowing between the retainer 166and interior surface 144.

Seal 136 is positioned in channel 142 between retainer 166 and the uppersurface 146 of transfer plate 108. The seal 136 includes a disk shapedbase 184 and a cylindrical protrusion 186 integral with and extendingupward from the base 184. An opening 188 extends through the center ofthe seal 136 and is enclosed by an interior surface 190. A flange 192extends outward from the base 184 of the seal 136 and includes aperipheral surface 194 that sealingly engages the interior surface 144of the valve body 106. The protrusion 186 includes an outer surface 196and a pair of rings 198 and 200 that are integral with and extendoutward from surface 196. Rings 198 and 200 sealingly engage the ring174 on retainer 166. Referring to FIG. 5D, the base 184 has a lowersurface 202 with five radial grooves formed therein one of which isshown as 204. The grooves 204 extend from an outer peripheral edge 206of base 184 to opening 188. The grooves 204 are designed to allow air toeasily reach all portions of the base 184 and flange 192 of seal 136. Itis within the scope of the invention for the seal 136 to have more orless than five grooves 204, including no grooves 204, and for thegrooves 204 to be spiral shaped instead of radial. It is also within thescope of the invention for the seal 136 to have some structure besidesgrooves that allows air to easily reach all portions of the base 184 andflange 192.

A valve chamber 208 is enclosed by the seal 136 and valve body 106.Rings 198 and 200 and flange 192 on seal 136 are in sealing engagementwith valve body 106 to prevent fluid from entering or exiting valvechamber 208. Spring 138 is positioned within valve chamber 208 betweenretainer 166 and seal 136. The spring 138 is positioned around ring 174to retain it in place within the chamber 208. One end of the spring 138abuts retainer 166 and the other end of the spring 138 abuts an uppersurface 210 of the base 184 of seal 136. The valve chamber 208 is not influid communication with spring chamber 58 or service brake pressurechamber 38.

The seal 136 is moveable between an open position, as shown in FIG. 5Ain which fluid can flow between the spring chamber 58 and the servicebrake pressure chamber 38 through the channel 142 of the valve body 106and the opening 188 in the seal 136, and a closed position, as shown inFIG. 5B in which fluid is blocked from flowing between the springchamber 58 and service brake pressure chamber 38. When the seal 136 isin its closed position, the opening 188 in seal 136 receives the plug176 on retainer 166 and the interior surface 190 sealingly engages theplug 176 to prevent fluid from flowing between the two. The seal 136 isbiased to its open position by spring 138. The seal 136 moves from itsopen position to its closed position when the pressure in service brakepressure chamber 38 increases to a threshold level at which the forceexerted on the lower surface 202 of seal 136 due to the pressure inpressure chamber 38 acting on the surface area of the lower surface 202is greater than the net force exerted on the upper surface 210 of seal136 due to the pressure in valve chamber 208 acting on the surface areaof the upper surface 210 and the biasing force of spring 138. When theseal 136 is in its closed position, pressure chamber 38 can bepressurized to activate the service brake actuator 12 withoutundesirably pressurizing the spring chamber 58. Spring 138 is optionalsuch that the seal 136 moves to its closed position when the forceexerted on the lower surface 202 of seal due to the pressure in pressurechamber 38 exceeds the force exerted on the upper surface 210 of seal136 due to the pressure in valve chamber 208.

The configuration of the channel 142 within valve body 106 and lowersurface 202 of seal 136 allow fluid from the pressure chamber 38 to flowunder the seal 136 and cause it to move to its closed position when thepressure in pressure chamber 38 reaches a threshold level as describedabove. Specifically, the diameter of the lower vertical section 158 ofthe channel increases moving upward from the lower surface 148 to theupper surface 146 of transfer plate 108 so that air flowing through thesection 158 reaches a larger portion of the lower surface 202 of seal136. Referring to FIG. 5D, the grooves 204 on the lower surface 202 ofseal 136 direct air contacting the lower surface 202 toward the outerperipheral edge 206 of the base 184 and in the gap between the outerperipheral edge 206 and the flange 192. Thus, when air flows intopressure chamber 38 through inlet port 50 the configuration of the seal136 and valve body 106 allows that air to contact the entire lowersurface 202 of the seal 136 for raising the seal 136 to its closedposition when the pressure in the pressure chamber 38 increases to athreshold level that exerts a force on the lower surface 202 of the seal136 that is greater than the net force exerted on the upper surface 210of seal 136 due to the pressure in valve chamber 208 and the biasingforce of spring 138.

Because the valve chamber 208 is not in fluid communication with servicebrake pressure chamber 38, movement of the seal 136 is not dependent onthe rate of flow of fluid between the spring chamber 58 and pressurechamber 38, as is the case with conventional pneumatic brake actuatortwo way control valves. Further, movement of the seal 136 is notdependent on the pressure differential between the spring chamber 58 andservice brake pressure chamber 38. The control valve 104 is a pilotoperated valve with the pilot pressure being the pressure in the servicebrake pressure chamber 38. Therefore, seal 136 will close when thepressure in service brake pressure chamber 38 reaches a threshold levelno matter how slowly the pressure in pressure chamber 38 rises.Accordingly, movement of the seal 136 is solely dependent on thepressure differential between the service brake pressure chamber 38 andthe valve chamber 208 and the biasing force exerted on the seal 136 byspring 138. When the pressure differential causes a net force to beexerted on the lower surface 202 of seal 136 that is greater than thebiasing force of spring 138, the seal 136 moves to its closed position.

While seal 136 and valve body 106 are preferably shaped as describedabove and shown in FIGS. 5A-D, it is within the scope of the inventionfor the seal 136 and valve body 106 to have a different construction.For example, it is within the scope of the invention for the seal 136 tohave any type of first sealing surface instead of surface 190 thatengages the valve body 106 when the seal is in its closed position, andany type of second and third sealing surfaces instead of surface 194 andring 198 that engage the valve body 106 to seal the valve chamber 208from the spring chamber 58 and the service brake pressure chamber 38.

Nine alternative embodiments of control valves 300, 400, 500, 600, 700,800, 900, 1000, and 1100 are shown in FIGS. 6A-14C and described below.Each of these alternative embodiments can be used in brake actuator 10in place of control valve 104 or in a piston type spring brake actuator.When used in brake actuator 10, each of the control valves 300, 400,500, 600, 700, 800, 900, 1000, and 1100 preferably threads withinactuator tube 82 and forms a seal with actuator tube 82 in the samemanner as described above with respect to control valve 104. Thespecific embodiments of control valves described in this application areexemplary only as other types of control valves fall within the scope ofthe present invention.

Referring to FIGS. 6A-6C, an alternative embodiment of control valve isshown generally as 300. Control valve 300 includes a valve body 302having a transfer plate 304 that is joined to a cylindrical protrusion306. The cylindrical protrusion 306 has a threaded side wall 308 thatengages threads 114 on actuator tube 82 (FIG. 1). A diaphragm seal 310and spring 312 are positioned inside a channel 314 defined by aninterior surface 316 of the valve body 302. The transfer plate 304 ofthe valve body 302 has upper and lower surfaces 318 and 320 joined by aside wall 322. The cylindrical protrusion 306 of the valve body 302 hasupper and lower surfaces 324 and 326 joined by threaded side wall 308.The lower surface 326 of the protrusion 306 is joined to the uppersurface 324 of the transfer plate 304. The channel 314 through the valvebody 302 includes a pair of holes 328 and 330 through upper surface 324,an upper cylindrical section 332 in fluid communication with the holes328 and 330, and a lower cylindrical section 334. A groove 336 is alsoformed in the lower surface 320 of the transfer plate 304.

The valve body 302 includes a retainer 338 that is positioned within thechannel 314 for retaining seal 310 within the channel 314. The retainer338 is preferably press fit into the channel 314. The retainer 338 iscylindrical and includes a hole 340 through its center. The retainer hasupper and lower surfaces 342 and 344 and a side wall 346. A groove 348is formed in lower surface 344 that is aligned with groove 336 intransfer plate 304.

Seal 310 is positioned in channel 314 between retainer 338 and the uppersurface 324 of protrusion 306. The seal 310 includes a diaphragm 350 anda cylindrical protrusion 352 extending upward from the diaphragm 350. Aflange 354 extends from the peripheral edge of the diaphragm 350. Theflange 354 is clamped and sealed between the upper surface 342 ofretainer 338 and a ledge 356 of interior surface 316. An opening 358extends through the center of the seal 310 and is enclosed by aninterior surface 360. The protrusion 352 includes an outer surface 362and a ring 364 that is integral with and extends outward from surface362. Ring 364 sealingly engages a portion of the interior surface 316 ofvalve body 302.

A valve chamber 366 is enclosed by the seal 310 and valve body 302. Ring364 and flange 354 on seal 310 are in sealing engagement with valve body302 to prevent fluid from entering or exiting valve chamber 366. Spring312 is positioned within valve chamber 366 between seal 310 and aportion of interior surface 316. One end of the spring 312 abutsinterior surface 316 and the other end of the spring 312 abuts thediaphragm 350 of seal 310. The valve chamber 366 is not in fluidcommunication with spring chamber 58 or service brake pressure chamber38.

The seal 310 moves between an open position, as shown in FIG. 6A inwhich fluid can flow between the spring chamber 58 and the service brakepressure chamber 38 (FIG. 1) through the channel 314 of the valve body302, the opening 358 in the seal 310, and the hole 340 in retainer 338,and a closed position, as shown in FIG. 6B in which fluid is blockedfrom flowing between the spring chamber 58 and service brake pressurechamber 38. As the seal 310 moves between its open and closed positions,the diaphragm 350 of seal flexes while the flange 354 remains stationaryand clamped between retainer 338 and ledge 356. Preferably, the seal 310is made from a flexible, resilient material capable of flexing as shownin FIGS. 6A and 6B. When the seal 310 is in its closed position, theopening 358 in seal 310 receives a plug 368 on valve body 302 and theinterior surface 360 sealingly engages the plug 368 to prevent fluidfrom flowing between the two. The seal 310 is biased to its openposition by spring 312. As described above in connection with controlvalve 104, the seal 310 moves from its open position to its closedposition when the pressure differential between the service brakepressure chamber 38 and valve chamber 366 causes a net force to beexerted on the lower surface of seal 310 that is greater than the forceexerted on the seal 310 by spring 312.

Another alternative embodiment of control valve 400 is shown in FIGS.7A-7C. Control valve 400 is similar to control valve 104. Accordingly,only the major differences are discussed herein. Control valve 400 has avalve body 402, and a seal 404, retainer 406, and spring 408 positionedwithin a channel 410 in the valve body 402. Valve body 402 has a bottomsurface 412 that is slightly different than the valve body 106 ofcontrol valve 104. Bottom surface 412 has a groove 414 formed thereinfor enhancing fluid flow to seal 404. Seal 404 has a flange 416 andrings 418 and 420 that sealingly engage valve body 402 to create a valvechamber 422 containing spring 408 that is sealed from spring chamber 58and pressure chamber 38 (FIG. 1).

The main difference between control valve 400 and control valve 104 isthat the seal 404 of control valve 400 has a cylinder 424 extendingupward from an upper surface 426 of the seal 404. The cylinder 424includes an upper sealing surface 428 that engages retainer 406 andblocks an opening 430 in the retainer 406 when the seal 404 is in itsclosed position, as shown in FIG. 7B. The seal 404 has an opening 432that is in fluid communication with opening 430 when the seal 404 is inits open position shown in FIG. 7A. The seal 404 also includes fourquarter circular shaped protrusions 434 a, 434 b, 434 c, and 434 d (FIG.7C) each joined to and extending between the upper surface 426 andcylinder 424. There are openings, two of which are shown as 436 a and436 b in FIG. 7A, between adjacent protrusions 434 a, 434 b, 434 c, and434 d that are in fluid communication with opening 432.

A filter 438 is securely attached on the top surface of the valve body402. The filter 438 is preferably made from a synthetic, polymeric orother type of filter material and may be attached to the valve body 402with a pressure sensitive adhesive backing. Preferably, the filter 438is a porous and gas permeable polymeric membrane having hydrophobic andoleophobic properties and a pore size chosen based on the size of debrispassing through the filter 438. One acceptable filter 438 comprises atreated, expanded polytetrafluoroethylene (PTFE) having a pore size ofone micron, available from W. L. Gore and Associates and sold under thebrand name Gore-Tex®. Alternatively, filter 438 may be constructed froma synthetic felt having a pore size of approximately 50 microns. Othertypes of filters are also within the scope of the present invention.Further, filter 438 may be attached to the top of any of the controlvalves shown in FIGS. 5A-13C.

Referring to FIGS. 8A-8B, an alternative embodiment of control valve isshown generally as 500. Control valve 500 is substantially identical tocontrol valve 400 shown in FIGS. 7A-7C. Accordingly, only thedifferences between the two are discussed in detail herein. Controlvalve 500 includes a seal 502 with a cylinder 504 extending upward froman upper surface of the seal 502. An end of the cylinder 504 has amushroom shaped head 506 that is received by an opening 508 in retainer510 when the seal 502 is in its closed position as shown in FIG. 8B. Aperipheral edge of the head 506 sealingly engages a surface 512 ofretainer 510 surrounding opening 508 when the seal 502 is in its closedposition. Seal 502 differs from seal 404 of control valve 400 because aportion of seal 502 is received by the opening 508 in the retainer 510when in its closed position while no portion of seal 404 is received bythe opening 430 in retainer 406 when in its closed position.

An alternative embodiment of valve 600 is shown in FIGS. 9A-9C. Controlvalve 600 includes a valve body 602 having a transfer plate 604 that isjoined to a cylindrical protrusion 606. The cylindrical protrusion 606has a threaded side wall 608 that engages threads 114 on actuator tube82 (FIG. 1). A seal, or piston, 610 and spring 612 are positioned insidea channel 614 defined by an interior surface 616 of the valve body 602.The transfer plate 604 of the valve body 602 has upper and lowersurfaces 618 and 620 joined by a side wall 622. The cylindricalprotrusion 606 of the valve body 602 has upper and lower surfaces 624and 626 joined by threaded side wall 608. The lower surface 626 of theprotrusion 606 is joined to the upper surface 618 of the transfer plate604. The channel 614 through the valve body 602 includes an uppercylindrical section 628, a lower cylindrical section 630, and ahorizontal passage 632 through the side wall 608 of the protrusion 606.The channel 614 includes an inlet 634 in the upper surface 624 ofprotrusion 606 and an outlet 636 in side wall 608. A groove 638 isformed in the lower surface 620 of the transfer plate 604.

The valve body 602 includes a retainer 640 that is positioned within thechannel 614 for retaining seal 610 within the channel 614. The retainer640 is preferably press fit into the lower section 630 of the channel614 to retain seal 610 therein. As shown in FIG. 9C, the retainer 640 iscircular having upper and lower surfaces 642 and 644 and a side wall646. Side wall 646 includes two flat edges 648 and 650 formed atopposing sides of the side wall 646. Slots 652 and 654 are formed in theside wall 646 at edges 648 and 650, respectively. As shown in FIG. 9A,the slots 652 and 654 are aligned with the groove 638 in the bottomsurface 620 of valve body 602 for providing a continuous flow passagefrom the bottom surface 620 of valve body 602 through retainer 640 toseal 610. The lower surface 644 of the retainer 640 is flat and flushwith the bottom surface 620 of the transfer plate 604.

Seal 610 is positioned in channel 614 between retainer 640 and the uppersurface 624 of protrusion 606. The seal 610 includes a disk shaped base656 and a cylindrical protrusion 658 extending upward from base 656. Thebase 656 is positioned in the lower section 630 of channel 614, and theprotrusion 658 extends upward into the upper section 628 of channel 614.Referring to FIG. 9C, a groove 660 is formed in base 656 for receivingan o-ring seal 662, and grooves 664 and 666 are formed in protrusion 658for receiving o-ring seals 668 and 670, respectively. Seal 662 sealinglyengages a portion of interior surface 616 surrounding lower section 630of channel 614, and seals 668 and 670 sealingly engage a portion ofinterior surface 616 surrounding upper section 628 of channel 614. Theseal 610 is preferably made from a rigid or semi-rigid material.

A valve chamber 672 is enclosed by the seal 610 and valve body 602.Seals 662, 668, and 670 are in sealing engagement with valve body 602 toprevent fluid from entering or exiting valve chamber 672. Spring 612 ispositioned within valve chamber 672 between seal 610 and valve body 602.One end of the spring 612 abuts interior surface 616 and the other endof the spring 612 abuts the base 656 of seal 610. The valve chamber 672is not in fluid communication with spring chamber 58 or service brakepressure chamber 38 (FIG. 1).

The seal 610 moves between an open position, as shown in FIG. 9A inwhich fluid can flow between the spring chamber 58 and the service brakepressure chamber 38, and a closed position, as shown in FIG. 9B in whichfluid is blocked from flowing between the spring chamber 58 and servicebrake pressure chamber 38. When actuator tube 82, shown in FIG. 1, isused with control valve 600, the actuator tube 82 is preferably modifiedto have an opening (not shown) through its side wall 84 that is alignedwith the outlet 636 in the side wall 608 of protrusion 606. The opening(not shown) in the actuator tube 82 is in fluid communication with theservice brake pressure chamber 38. When the seal 610 is in its openposition, fluid can flow from spring chamber 58 to service brakepressure chamber 38 through inlet 634, horizontal channel 632, outlet636 and the opening (not shown) in actuator tube 82. When the seal 610is in its closed position, seal 668 prevents fluid from flowing betweenthe spring chamber 58 and service brake pressure chamber 38. The seal610 is biased to its open position by spring 612. As described above inconnection with control valve 104, the seal 610 moves from its openposition to its closed position when the pressure differential betweenthe service brake pressure chamber 38 and valve chamber 672 causes a netforce to be exerted on the lower surface of seal 610 that is greaterthan the force exerted on the seal 610 by spring 612.

Referring to FIG. 10, an alternative embodiment of control valve isshown as 700. Control valve 700 is substantially similar to controlvalve 600. Accordingly, control valve 700 is only described herein tothe extent that it differs from control valve 600. While control valve600 has a horizontal channel 632 with an outlet 636 in the side wall 608of protrusion 606, control valve 700 has a horizontal channel 702 thatis in fluid communication with a vertical channel 704 that has an outlet706 in the lower surface 708 of the transfer plate 710 of the valve body712. The outlet 706 is positioned within a groove 714 in the lowersurface 708. When the valve 700 is in the open position shown in FIG.10, fluid can flow from spring chamber 58 to service brake pressurechamber 38 (FIG. 1) through an inlet 716, horizontal channel 702,vertical channel 704, and outlet 706. The seal, or piston, 718 of thevalve 700 moves upward into its closed position in the same manner asthe seal 610 of valve 600 to block fluid from flowing through channel702.

FIGS. 11A-11C show another alternative embodiment of control valve 800in accordance with the present invention. Control valve 800 has a valvebody 802 with a transfer plate 804 that is joined to a cylindricalprotrusion 806. The protrusion 806 has a threaded side wall 808 thatengages threads on actuator tube 82. The valve body 802 defines achannel 810 including an upper cylindrical section 812 surrounded byside wall 808 and a lower cylindrical section 814 positioned withintransfer plate 804. The transfer plate 804 has upper and lower surfaces816 and 818, respectively, and a side wall 819, and the protrusion 806has upper and lower surfaces 820 and 822, respectively. The uppersurface 816 of transfer plate 804 is joined to the lower surface 822 ofprotrusion 806. A groove 824 is formed in the lower surface 818 oftransfer plate 804.

A seal, or piston, 826, spring 828, and retainer 830 are positionedwithin the upper section 812 of channel 810. The retainer 830 isgenerally cylindrical and has an upper surface 832, a side wall 834, anda lower edge 836. The retainer 830 has a cavity 838 with a lowercylindrical section 840 adjacent lower edge 836, an annular section 842for retaining spring 828, and first, second, and third upper cylindricalsections 844, 846, and 848. Second cylindrical section 846 has a greaterdiameter than third cylindrical section 848 such that an annular surface850 is positioned between the two sections. A horizontal channel 852extends from the second cylindrical section 846 to a vertical groove 854in the side wall 834 of the retainer 830. There is also a groove 856formed in the side wall 834 of retainer 830 for receiving a seal 858that prevents fluid from flowing between retainer 830 and valve body802.

The seal 826 has a disk shaped base 860 and a cylindrical protrusion 862extending upward from the base 860. Referring to FIG. 11C, a groove 864is formed in base 860 for receiving a delta seal 866, and a pair ofgrooves 868 and 870 are formed in protrusion 862 for receiving squarering seals 872 and 874, respectively. The base 860 is positioned in thelower cylindrical section 840 of the cavity 838 within retainer 830. Theprotrusion 862 extends upward through the first and second cylindricalsections 844 and 846 of the cavity 838 within retainer 830. The seal 826is preferably made from a rigid or semi-rigid material.

A valve chamber 876 is enclosed by the seal 826 and retainer 830. Seals866 and 874 are in sealing engagement with the retainer 830 to preventfluid from entering or exiting the valve chamber 876. The spring 828 ispositioned within the valve chamber 876 between a portion of theretainer 830 and the seal 826 for biasing the seal 826 to its openposition shown in FIG. 11A.

The seal 826 is moveable between its open position shown in FIG. 11A andthe closed position shown in FIG. 11B. In its open position, fluid canflow between the spring chamber 58 and the service brake pressurechamber 38 (FIG. 1) through the second and third upper sections 846 and848 of the cavity 838 in retainer 830, the horizontal channel 852,vertical groove 854, the space between seal 826 and the upper surface816 of transfer plate 804, and the lower cylindrical section 814 ofchannel 810. When the seal 826 is in its closed position, as shown inFIG. 11B, the square ring seal 872 engages the annular surface 850 toprevent fluid from flowing between the second and third upper sections846 and 848 thereby preventing fluid from flowing between the springchamber 58 and the service brake pressure chamber 38. As described abovein connection with control valve 104, the seal 826 moves from its openposition to its closed position when the pressure differential betweenthe service brake pressure chamber 38 and valve chamber 876 causes a netforce to be exerted on the lower surface of seal 826 that is greaterthan the force exerted on the seal 826 by spring 828.

Referring to FIGS. 12A-12C, an alternative embodiment of control valveis shown generally as 900. Control valve 900 has a valve body 902 havinga transfer plate 904 that is joined to a cylindrical protrusion 906. Thecylindrical protrusion 906 has a threaded side wall 908 that engagesthreads 114 on actuator tube 82 (FIG. 1). A seal, or piston, 910 andspring 912 are positioned inside a channel 914 defined by an interiorsurface 916 of the valve body 902. The transfer plate 904 of the valvebody 902 has upper and lower surfaces 918 and 920 joined by a side wall922. The cylindrical protrusion 906 of the valve body 902 has upper andlower surfaces 924 and 926 joined by threaded side wall 908. The lowersurface 926 of the protrusion 906 is joined to the upper surface 918 ofthe transfer plate 904. The channel 914 through the valve body 902includes a lower cylindrical section 928, an annular section 930 forretaining spring 912, and first, second, and third upper cylindricalsections 932, 934, and 936. Second cylindrical section 934 has a greaterdiameter than third cylindrical section 936 such that an annular surface938 is positioned between the two sections. A groove 940 is formed inthe lower surface 920 of the transfer plate 904.

The valve body 902 includes a retainer 942 that is positioned within thechannel 914 for retaining seal 910 within the channel 914. The retainer942 is preferably press fit into the lower section 928 of the channel914 to retain seal 910 therein. As shown in FIG. 12C, the retainer 942is circular having upper and lower surfaces 944 and 946 and a side wall948. Side wall 948 includes two flat edges 950 and 952 formed atopposing sides of the side wall 948. Slots 954 and 956 are formed in theside wall 948 at edges 950 and 952, respectively. As shown in FIG. 12A,the slots 954 and 956 are aligned with the groove 940 in the bottomsurface 920 of valve body 902 for providing a continuous flow passagefrom the bottom surface 920 of valve body 902 through retainer 942 toseal 910. The lower surface 946 of the retainer 942 is flat and flushwith the bottom surface 920 of the transfer plate 904.

Seal 910 is positioned in channel 914 between retainer 942 and the uppersurface 924 of protrusion 906. The seal 910 includes a disk shaped base958 and a cylindrical protrusion 960 extending upward from base 958. Thebase 958 is positioned in the lower section 928 of channel 914, and theprotrusion 960 extends upward into the first and second upper sections932 and 934 of channel 914. Referring to FIG. 12C, a groove 962 isformed in base 958 for receiving an o-ring seal 964, and grooves 966 and968 are formed in protrusion 960 for receiving o-ring seals 970 and 972,respectively. Seal 964 sealingly engages a portion of interior surface916 surrounding lower section 928 of channel 914, and seal 972 sealinglyengages a portion of interior surface 916 surrounding first uppersection 932 of channel 914. Referring to FIG. 12A, there is a horizontalchannel 974 formed in the protrusion 960 between seals 970 and 972.Horizontal channel 974 is in fluid communication with a vertical channel976 that extends downward through the base 958 of seal 910. The seal 910is preferably made from a rigid or semi-rigid material.

A valve chamber 978 is enclosed by the seal 910 and valve body 902.Seals 964 and 972 are in sealing engagement with the valve body 902 toprevent fluid from entering or exiting the valve chamber 978. The spring912 is positioned within the valve chamber 978 between a portion of thevalve body 902 and the seal 910 for biasing the seal 910 to its openposition shown in FIG. 12A.

The seal 910 is moveable between its open position shown in FIG. 12A andthe closed position shown in FIG. 12B. In its open position, fluid canflow between the spring chamber 58 and the service brake pressurechamber 38 (FIG. 1) through the second and third upper sections 934 and936 of channel 914, the horizontal and vertical channels 974 and 976 inseal 910, and the space between seal 910 and retainer 942. When the seal910 is in its closed position, as shown in FIG. 12B, the o-ring seal 970engages the annular surface 938 to prevent fluid from flowing betweenthe second and third cylindrical sections 934 and 936 thereby preventingfluid from flowing between the spring chamber 58 and the service brakepressure chamber 38. As described above in connection with control valve104, the seal 910 moves from its open position to its closed positionwhen the pressure differential between the service brake pressurechamber 38 and valve chamber 978 causes a net force to be exerted on thelower surface of seal 910 that is greater than the force exerted on theseal 910 by spring 912. A filter 980 is securely attached on the topsurface of the valve body 902. Filter 980 is preferably similar to thefilter 438 of control valve 400.

FIGS. 13A-13C show an alternative embodiment of control valve 1000 inaccordance with the present invention. Control valve 1000 has a valvebody 1002 with a transfer plate 1004 that is joined to a cylindricalprotrusion 1006. The protrusion 1006 has a threaded side wall 1008 thatengages threads on actuator tube 82 (FIG. 1). The valve body 1002defines a channel 1010 including an upper cylindrical section 1012surrounded by side wall 1008 and a lower cylindrical section 1014positioned within transfer plate 1004. The transfer plate 1004 has upperand lower surfaces 1016 and 1018, respectively, and a side wall 1019,and the protrusion 1006 has upper and lower surfaces 1020 and 1022,respectively. The upper surface 1016 of transfer plate 1004 is joined tothe lower surface 1022 of protrusion 1006. A groove 1024 is formed inthe lower surface 1018 of transfer plate 1004.

A seal 1026, spring 1028, and retainer 1030 are positioned within theupper section 1012 of channel 1010. The retainer 1030 is generallycylindrical and has an upper surface 1032, a side wall 1034, and a loweredge 1036. The retainer 1030 has a cavity 1038 with a lower cylindricalsection 1040 adjacent lower edge 1036, an annular section 1042 forretaining spring 1028, and first, second, and third upper cylindricalsections 1044, 1046, and 1048. Second cylindrical section 1046 has agreater diameter than third cylindrical section 1048 such that anannular surface 1050 is positioned between the two sections. A groove1052 is formed in the side wall 1034 of retainer 1030 for receiving aseal 1054 that prevents fluid from flowing between retainer 1030 andvalve body 1002.

The seal 1026 has a disk shaped base 1056 and a cylindrical protrusion1058 extending upward from the base 1056. Referring to FIG. 13C, agroove 1060 is formed in base 1056 for receiving a delta seal 1062. Asealing ring 1064 extends outward from the middle of protrusion 1058.The end 1066 of protrusion 1058 is dome shaped. The base 1056 ispositioned in the lower cylindrical section 1040 of the cavity 1038within retainer 1030. The protrusion 1058 extends upward through thefirst and second cylindrical sections 1044 and 1046 of the cavity 1038within retainer 1030. Seal 1062 sealingly engages a portion of retainer1030, and sealing ring 1064 sealingly engages a portion of retainer1030. Referring to FIG. 13A, there is a horizontal channel 1068 formedin the protrusion 1058 between sealing ring 1064 and end 1066.Horizontal channel 1068 is in fluid communication with a verticalchannel 1070 that extends downward through the base 1056 of seal 1026.

A valve chamber 1072 is enclosed by the seal 1026 and retainer 1030.Seal 1062 and sealing ring 1064 are in sealing engagement with theretainer 1030 to prevent fluid from entering or exiting the valvechamber 1072. The spring 1028 is positioned within the valve chamber1072 between a portion of the retainer 1030 and the seal 1026 forbiasing the seal 1026 to its open position shown in FIG. 13A.

The seal 1026 is moveable between its open position shown in FIG. 13Aand the closed position shown in FIG. 13B. In its open position, fluidcan flow between the spring chamber 58 and the service brake pressurechamber 38 (FIG. 1) through the second and third upper sections 1046 and1048 of the cavity 1038 in retainer 1030, the horizontal channel 1068and vertical channel 1070 in seal 1026, and the lower cylindricalsection 1014 of channel 1010. When the seal 1026 is in its closedposition, as shown in FIG. 13B, the dome shaped end 1066 of seal 1026engages the annular surface 1050 of retainer 1030 to prevent fluid fromflowing between the second and third upper sections 1046 and 1048thereby preventing fluid from flowing between the spring chamber 58 andthe service brake pressure chamber 38. As described above in connectionwith control valve 104, the seal 1026 moves from its open position toits closed position when the pressure differential between the servicebrake pressure chamber 38 and valve chamber 1072 causes a net force tobe exerted on the lower surface of seal 1026 that is greater than theforce exerted on the seal 1026 by spring 1028.

Referring now to FIGS. 14A-14C, an alternative embodiment of controlvalve 1100 includes a valve body 1102 with a transfer plate 1104 and acylindrical protrusion 1106 joined to the transfer plate 1104. Thecylindrical protrusion 1106 has a threaded side wall 1108 that engagesthreads on actuator tube 82 (FIG. 1). The transfer plate 1104 has upperand lower surfaces 1110 and 1112 joined by a side wall 1114. Thecylindrical protrusion 1106 has upper and lower surfaces 1116 and 1118joined by threaded side wall 1108. The lower surface 1118 of theprotrusion 1106 is joined to the upper surface 1110 of the transferplate 1104. A channel 1120 is defined by an interior surface 1122 of thevalve body 1102. The channel 1120 includes an upper cylindrical section1124 that is enclosed by the side wall 1108 of protrusion 1106, a lowervertical section 1126 extending through the transfer plate 1104 fromupper surface 1110 to lower surface 1112, and a lower horizontal section1128 that extends through the transfer plate 1104 between openings 1130and 1132 in side wall 1114.

The valve body 1102 includes a retainer 1134 that is positioned in thechannel 1120, and is preferably press fit into the channel 1120. Theretainer 1134 has a disk shaped upper section 1136 that is supported bya ledge 1138 formed in the interior surface 1122. Concentric rings 1140,1142, and 1144 that are integral with upper section 1136 extend intochannel 1120. An opening 1146 extends through the center of retainer1134. The opening 1146 allows air to flow through the retainer 1134. Afilter 1148 is securely attached on the top surface of the valve body1102.

A seal 1150, spring 1152, and o-ring seal 1154 are positioned insidechannel 1120 between retainer 1134 and the upper surface 1110 oftransfer plate 1104. The retainer 1134 retains the seal 1150 within thechannel 1120. The o-ring seal 1154 is positioned between ring 1140 andthe interior surface 1122 to form a seal and prevent air from flowingbetween the retainer 1134 and interior surface 1122.

The seal 1150 includes a disk shaped base 1156 and a cylindricalprotrusion 1158 integral with and extending upward from the base 1156. Acylindrical plug 1160 is positioned in the center of the seal 1150, anda plurality of openings, one of which is shown as 1162, are positionedaround the plug 1160 and extend through the seal 1150. A flange 1164extends outward from the base 1156 of the seal 1150 and includes aperipheral surface 1166 that sealingly engages the interior surface 1122of the valve body 1102. The protrusion 1158 includes an outer surface1168 that sealingly engages the ring 1142 on retainer 1134. The base1156 has a lower surface with five radial grooves (not shown) formedtherein similar to those shown on the seal 136 in FIG. 5D. The channel1120 and lower surface of seal 1150 have a similar configuration asdescribed above in connection with valve 104 shown in FIGS. 5A-5D forallowing air to reach a larger portion of the bottom of seal 1150.

A valve chamber 1170 is enclosed by the seal 1150 and valve body 1102.The outer surface 1168 of protrusion 1158 and flange 1164 on seal 1150are in sealing engagement with valve body 1102 to prevent fluid fromentering or exiting valve chamber 1170. The valve chamber 1170 is not influid communication with spring chamber 58 or service brake pressurechamber 38. Spring 1152 is positioned within valve chamber 1170 betweenretainer 1134 and seal 1150. The spring 1152 is positioned around ring1142 to retain it in place within the chamber 1170. One end of thespring 1152 abuts retainer 1134 and the other end of the spring 1152abuts an upper surface 1172 of the base 1156 of seal 1150.

The seal 1150 is moveable between an open position, as shown in FIG. 14Bin which fluid can flow between the spring chamber 58 and the servicebrake pressure chamber 38 through the channel 1120 of the valve body1102 and the opening 1162 in the seal 1150, and a closed position, asshown in FIG. 14A in which fluid is blocked from flowing between thespring chamber 58 and service brake pressure chamber 38. When the seal1150 is in its closed position, the opening 1146 in retainer 1134receives a portion of the plug 1160 of seal 1150, which is slightlylarger than the opening 1146 so that it blocks the opening 1146 andprevents fluid from flowing between the two. The seal 1150 is biased toits open position by spring 1152. As described above in connection withcontrol valve 104, the seal 1150 moves from its open position to itsclosed position when the pressure differential between the service brakepressure chamber 38 and valve chamber 1170 causes a net force to beexerted on the lower surface of seal 1150 that is greater than the forceexerted on the seal 1150 by spring 1152.

While the following description of the operation of the brake actuator10 is applicable to use of the brake actuator 10 with any of the controlvalves 104, 300, 400, 500, 600, 700, 800, 900, 1000, and 1100 describedabove, only control valve 104 is referenced below for convenience.

In operation, the spring brake actuator 14 is moveable between theengaged position shown in FIG. 4 and the disengaged position shown inFIG. 2. When the vehicle on which brake actuator 10 is installed isparked for an extended period of time, the spring brake actuator 14 istypically in the engaged position shown in FIG. 4. In the engagedposition, pressure is released from the spring brake pressure chamber 56so that the compression spring 62 pushes the pressure plate 60 and thediaphragm 32 toward the adapter housing 20. As a result, the actuatortube 82 connected to the pressure plate 60 is pushed through the opening102 in the adapter housing 20 and the transfer plate 108 of the controlvalve 104 forces the diaphragm 30 and pressure plate 42 toward the endwall 16 a of the service brake actuator housing 16. This forces themajority of pushrod 40 out of the housing 16 and actuates the vehicle'sparking or emergency brakes. When the spring brake actuator 14 is in theengaged position shown in FIG. 4, the vehicle on which the brakeactuator 10 is installed cannot move. To allow the vehicle to move, thespring 62 must be retracted either by pressurizing the spring brakepressure chamber 56, as shown in FIG. 2, or by mechanically retractingthe spring 62 with caging bolt 122, as shown in FIG. 1 and describedabove. Mechanical retraction of spring 62 with caging bolt 122 istypically only necessary during assembly of the brake actuator 10 and/orwhen mechanical release of the actuator 10 is necessary due to a failureor absence of the compressed air system.

When spring brake pressure chamber 56 is pressurized, diaphragm 32 andpressure plate 60 retract spring 62 and compress it against housing wall18 a to move the spring brake actuator 14 to its disengaged position, asshown in FIG. 2. The movement of pressure plate 60 causes actuator tube82 to retract upward through opening 102 in adapter housing 20 therebyreleasing pressure on diaphragm 30 and pressure plate 42. Spring 48 thenbiases pressure plate 42 and pushrod 40 to the position shown in FIG. 2in which the vehicle's parking brakes are released. Bearing 94 allowsthe pressure plate 60 and actuator tube 82 to move with respect to thecaging bolt 122 from the position shown in FIG. 2 to the position shownin FIG. 4 while preventing damage to the pressure plate 60, actuatortube 82, and caging bolt 122. The inner surface 97 of the bearing 94 isin close contact with the threads of the caging bolt to guide movementof the pressure plate 60 and actuator tube 82. The inner surface 97 ofthe bearing 94 is preferably relatively smooth to minimize damage to thethreads of the caging bolt 122.

As spring brake pressure chamber 56 is pressurized to release thevehicle's parking brakes, the volume of the pressure chamber 56increases due to the retraction of spring 62. As the volume of chamber56 increases, the volume of spring chamber 58 decreases therebyincreasing the pressure of the air contained therein. The pressurizedair in the spring chamber 58 is fluidly connected to the control valve104 through the bearing 94 and the interior space 98 of the actuatortube 82. As long as service brake pressure chamber 38 has not beenpressurized while the spring brake actuator 14 is actuated, the seal 136in the control valve 104 is in its open position, shown in FIG. 5A, whenthe spring brake actuator 14 is actuated. The seal 136 remains in itsopen position as spring brake pressure chamber 56 is pressurized, whichallows the pressurized air in spring chamber 58 to flow through controlvalve 104 into service brake pressure chamber 38. That air can bereleased from service brake pressure chamber 38 through inlet port 50.In this manner, the pressure build-up in the spring chamber 58 iseffectively released by operation of the control valve 104 of theinvention, without providing a vent opening in the spring chamber 58.

When the spring brake actuator 14 is applied by exhausting thepressurized air from the spring brake pressure chamber 56 of the springbrake actuator 14, the volume of the spring chamber 58 expands causingthe pressure within the chamber 58 to drop. Air flows through thecontrol valve 104 from the service brake pressure chamber 38 into thespring chamber 58 in order to prevent the formation of a vacuum in thespring chamber 58 and allow the spring brake actuator 14 to engage in atimely manner. During engagement of the spring brake actuator 14, theseal 136 remains in its open position to allow air to flow through thecontrol valve 104. The spring 138 that biases the seal 136 to its openposition is configured so that it is able to maintain the seal 136 inits open position during engagement of the spring brake actuator 14 byresisting force exerted on the seal 136 due to the pressure differentialbetween the spring chamber 58 and valve chamber 208 caused by expansionof the spring chamber 58.

When the spring brake actuator 14 is in the disengaged position shown inFIGS. 2 and 3 and the vehicle on which the brake actuator 10 isinstalled is in transit, the service brake actuator 12 is utilized tobrake the vehicle. The service brake actuator 12 moves between thedisengaged position shown in FIG. 2 and the engaged position shown inFIG. 3. When in the disengaged position shown in FIG. 2, the pushrod 40is retracted to a position that does not actuate the vehicle's brakes.To actuate the vehicle's service brakes, air enters the service brakepressure chamber 38 through inlet port 50. As the pressure in chamber 38builds it forces diaphragm 30, pressure plate 42, and pushrod 40 towardend wall 16 a into the position shown in FIG. 3 thereby overcomingspring 48 and actuating the vehicle's service brakes.

As the pressure builds in service brake pressure chamber 38 and theservice brake actuator 12 moves from its disengaged position to itsengaged position, the seal 136 in control valve 104 moves from its openposition to its closed position in order to prevent the undesirableincrease of pressure in spring chamber 58. Because the control valve 104is a pilot operated valve that closes based on the pressure in servicebrake pressure chamber 38 regardless of the rate of flow of fluidthrough the valve 104 or the pressure differential between service brakepressure chamber 38 and spring chamber 58, the valve 104 is able toprevent the undesirable build up of pressure in spring chamber 58 evenwhen air is slowly introduced into pressure chamber 38 through inletport 50. This is in contrast to conventional pneumatic brake actuatorcontrol valves which are flow rate dependent and allow air to flowthrough them and pressurize the spring chamber when the service brakesare slowly applied. Because the control valves 104, 300, 400, 500, 600,700, 800, 900, and 1000 described herein are insensitive to the rate offlow of fluid moving through them and the pressure differential betweenthe spring chamber 58 and service brake pressure chamber 38, theyprevent pressure build up in the spring chamber 58 while the servicebrake actuator 12 is engaged, which prevents damage to the brakeactuator and vehicle's braking components caused by the simultaneousapplication of the service and spring brake actuators 12 and 14.

When the service brake actuator 12 is moved from its engaged position toits disengaged position by exhausting the air within service brakepressure chamber 38, the seal 136 in control valve 104 moves from itsclosed position to its open position to again allow air flow between thespring chamber 58 and pressure chamber 38.

As described above, one advantage of the sealed pneumatic brake actuator10 according to the invention is that the spring brake actuator 14 iscompletely sealed with respect to the atmosphere, which preventsmoisture from entering the spring chamber 58 and corroding the spring62. The control valve 104 with two-way communication or breathingability permits the relief of pressure build up in the sealed springchamber 58 and it also prevents a vacuum from forming in the springchamber 58 when the spring brake actuator 14 is engaged. Therefore,spring 62 does not need an enhanced spring force to overcome the effectsof vacuum generation in the spring chamber 58, as is common with someconventional pneumatic brake actuators.

While all of the control valves 104, 300, 400, 500, 600, 700, 800, 900,1000, and 1100 described herein include a spring that biases the seal ofthe valve to its open position, it is within the scope of the inventionfor something other than a spring to bias the seal of each valve to itsopen position. For example, the seal itself could be manufactured from amaterial and configured in such a way that it biases itself to its openposition and rebounds to that position when the pressure in servicebrake pressure chamber 38 subsides. Alternatively, during constructionof each of the valves described herein, the valve chamber (e.g., valvechamber 208 shown in FIG. 5A) that is enclosed by the seal and valvebody may be pressurized with a fluid, which pressure biases the seal toits open position so that no spring is necessary to bias the seal to itsopen position. Additionally, it is within the scope of the invention forany of the o-ring seals, delta seals, and square seals described aboveand shown in the drawings to be interchanged with each other or withquad ring seals.

From the foregoing it will be seen that this invention is one welladapted to attain all ends and objectives herein-above set forth,together with the other advantages which are obvious and which areinherent to the invention.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that allmatters herein set forth or shown in the accompanying drawings are to beinterpreted as illustrative, and not in a limiting sense.

While specific embodiments have been shown and discussed, variousmodifications may of course be made, and the invention is not limited tothe specific forms or arrangement of parts and steps described herein,except insofar as such limitations are included in the following claims.Further, it will be understood that certain features and subcombinationsare of utility and may be employed without reference to other featuresand subcombinations. This is contemplated by and is within the scope ofthe claims.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A pneumatic brake actuator, comprising: a spring brakeactuator comprising a sealed spring chamber and a spring brake pressurechamber; a service brake actuator coupled with the spring brake actuatorand comprising a service brake pressure chamber; an actuator tubecomprising a side wall that defines an interior space which is in fluidcommunication with the spring chamber, wherein the actuator tubecomprises a first end positioned adjacent the spring chamber and asecond end positioned adjacent the service brake pressure chamber,wherein the second end presents an opening; a valve body that is coupledto the second end of the actuator tube, wherein the valve body defines achannel that is in fluid communication with the opening; and a sealpositioned within the channel in the valve body, wherein the seal andthe valve body enclose a valve chamber that is not in fluidcommunication with the spring chamber and the service brake pressurechamber such that fluid does not flow from the spring chamber throughthe valve chamber to the service brake pressure chamber, wherein theseal is moveable between an open position in which fluid can flowthrough the channel between the spring chamber and the service brakepressure chamber and a closed position in which fluid is blocked fromflowing through the channel between the spring chamber and the servicebrake pressure chamber.
 2. The brake actuator of claim 1, wherein thevalve body is at least partially positioned within the interior space ofthe actuator tube through the opening.
 3. The brake actuator of claim 1,wherein the seal is biased to the open position.
 4. The brake actuatorof claim 1, wherein the seal comprises a first surface that is in fluidcommunication with the service brake pressure chamber, and wherein theseal comprises a second surface that is in fluid communication with thevalve chamber.
 5. The brake actuator of claim 4, wherein a pressure inthe service brake pressure chamber comprises a first pressure, and apressure in the valve chamber comprises a second pressure, wherein afirst force is exerted on the first surface due to the first pressureacting on the first surface, wherein a second force is exerted on thesecond surface due to the second pressure acting on the second surface,and wherein the seal moves from the open position to the closed positionwhen the first force is greater than the second force.
 6. The brakeactuator of claim 5, further comprising a spring that exerts a thirdforce on the second surface, and wherein the seal moves from the openposition to the closed position when the first force exceeds the sum ofthe second and third forces.
 7. The brake actuator of claim 1, whereinfluid flows from the spring chamber through the channel to the servicebrake pressure chamber when the volume of the spring chamber decreasesand the service brake pressure chamber is not pressurized.
 8. The brakeactuator of claim 1, wherein the seal comprises an opening through whichfluid flows when the seal is in the open position, and wherein theopening extends through the seal in a direction that is aligned with adirection of movement of the seal.
 9. The brake actuator of claim 1,wherein the seal comprises a first sealing surface that engages thevalve body when the seal is in its closed position to block fluid fromflowing through the channel, and wherein the seal comprises second andthird sealing surfaces each of which engages the valve body to seal thevalve chamber from the spring chamber and the service brake pressurechamber.
 10. The brake actuator of claim 9, wherein the valve bodycomprises: an interior surface surrounding the channel, a transfer platecomprising upper and lower surfaces joined by a side wall, a cylindricalprotrusion comprising upper and lower surfaces joined by a side wall,wherein the lower surface of the protrusion is joined to the uppersurface of the transfer plate, wherein the protrusion is coupled withthe side wall of the actuator tube and positioned within the interiorspace of the actuator tube, and a retainer that is positioned within thechannel to retain the seal within the channel.
 11. The brake actuator ofclaim 10, wherein the seal presents an opening that is in fluidcommunication with the spring chamber and the service brake pressurechamber when the seal is in its open position, wherein the first sealingsurface surrounds the opening, wherein the seal is positioned within thechannel between the retainer and the upper surface of the transferplate, wherein the retainer comprises a plug that is received by theopening in the seal and engages the first sealing surface when the sealis in its closed position, and wherein the second sealing surfaceengages the interior surface of the valve body and the third sealingsurface engages the retainer.
 12. The brake actuator of claim 10,wherein the seal presents an opening that is in fluid communication withthe spring chamber and the service brake pressure chamber when the sealis in its open position, wherein the first sealing surface surrounds theopening, wherein the seal is positioned within the channel between theretainer and the upper surface of the protrusion, wherein the valve bodycomprises a plug that is received by the opening in the seal and engagesthe first sealing surface when the seal is in its closed position,wherein the second sealing surface comprises a flange that is positionedbetween the retainer and the interior surface of the valve body and thethird sealing surface engages the interior surface of the valve body,and wherein the seal comprises a diaphragm joined to the flange, whereinthe diaphragm flexes when the seal moves from its open position to itsclosed position.
 13. The brake actuator of claim 10, wherein each of theseal and the retainer presents an opening that is in fluid communicationwith the spring chamber and the service brake pressure chamber when theseal is in its open position, wherein the seal is positioned within thechannel between the retainer and the upper surface of the transferplate, wherein the first sealing surface engages the retainer and blocksthe opening in the retainer when the seal is in its closed position, andwherein the second sealing surface engages the interior surface of thevalve body and the third sealing surface engages the retainer.
 14. Thebrake actuator of claim 10, wherein each of the seal and the retainerpresents an opening that is in fluid communication with the springchamber and the service brake pressure chamber when the seal is in itsopen position, wherein the seal is positioned within the channel betweenthe retainer and the upper surface of the transfer plate, wherein thefirst sealing surface comprises a protrusion that is received by andblocks the opening in the retainer when the seal is in its closedposition, and wherein the second sealing surface engages the interiorsurface of the valve body and the third sealing surface engages theretainer.
 15. The brake actuator of claim 10, wherein there is anopening in the side wall of the actuator tube adjacent the second end,and wherein the channel comprises an inlet in the upper surface of theprotrusion and an outlet in the side wall of the protrusion, whichoutlet is in fluid communication with the opening in the side wall ofthe actuator tube.
 16. The brake actuator of claim 10, wherein thechannel comprises an inlet in the upper surface of the protrusion and anoutlet in the lower surface of the transfer plate.
 17. The brakeactuator of claim 1, wherein the seal is a pilot operated valve and apilot pressure operating the seal is a pressure in the service brakepressure chamber.
 18. The brake actuator of claim 1, wherein movement ofthe seal from the open position to the closed position is not dependenton the rate of flow of fluid between the spring chamber and the servicebrake pressure chamber.
 19. The brake actuator of claim 1, whereinmovement of the seal from the open position to the closed position isnot dependent on the difference between a pressure in the service brakepressure chamber and a pressure in the spring chamber, and wherein theseal is arranged to move between the open position and the closedposition based on the pressure in the service brake pressure chamber.20. The brake actuator of claim 19, wherein the seal is biased to theopen position.
 21. A pneumatic brake actuator, comprising: a springbrake actuator comprising a sealed spring chamber and a spring brakepressure chamber; a service brake actuator coupled with the spring brakeactuator and comprising a service brake pressure chamber; a valve bodythat defines a channel between the spring chamber and the service brakepressure chamber; and a seal positioned within the channel in the valvebody, wherein the seal and the valve body enclose a valve chamber thatis not in fluid communication with the spring chamber and the servicebrake pressure chamber such that fluid does not flow from the springchamber through the valve chamber to the service brake pressure chamber,wherein the seal is moveable between an open position in which fluid canflow through the channel between the spring chamber and the servicebrake pressure chamber and a closed position in which fluid is blockedfrom flowing through the channel between the spring chamber and theservice brake pressure chamber, wherein the seal comprises a firstsealing surface that engages the valve body when the seal is in itsclosed position to prevent fluid from flowing between the spring chamberand the service brake pressure chamber, and wherein the seal comprisessecond and third sealing surfaces each of which engages the valve bodyto seal the valve chamber from the spring chamber and the service brakepressure chamber.
 22. The brake actuator of claim 21, wherein the sealcomprises an opening through which fluid flows when the seal is in theopen position, and wherein the opening extends through the seal in adirection that is aligned with a direction of movement of the seal. 23.The brake actuator of claim 21, wherein a pressure in the service brakepressure chamber comprises a first pressure, and a pressure in the valvechamber comprises a second pressure, wherein the seal comprises a firstsurface that is in fluid communication with the service brake pressurechamber and a second surface that is in fluid communication with thevalve chamber, wherein a first force is exerted on the first surface dueto the first pressure acting on the first surface, wherein a secondforce is exerted on the second surface due to the second pressure actingon the second surface, and wherein the seal moves from the open positionto the closed position when the first force is greater than the secondforce.
 24. The brake actuator of claim 23, further comprising a springthat exerts a third force on the second surface, and wherein the sealmoves from the open position to the closed position when the first forceexceeds the sum of the second and third forces.
 25. The brake actuatorof claim 21, wherein movement of the seal from the open position to theclosed position is not dependent on the rate of flow of fluid betweenthe spring chamber and the service brake pressure chamber.
 26. The brakeactuator of claim 21, wherein the seal is biased to the open position.27. The brake actuator of claim 21, wherein the seal is arranged to movebetween the open position and the closed position based on a pressure inthe service brake pressure chamber.
 28. The brake actuator of claim 27,wherein the seal is biased to the open position.
 29. A pneumatic brakeactuator, comprising: a spring brake actuator comprising a sealed springchamber and a spring brake pressure chamber; a service brake actuatorcoupled with the spring brake actuator and comprising a service brakepressure chamber; a valve body that defines a channel between the springchamber and the service brake pressure chamber; and a seal positionedwithin the channel in the valve body, wherein the seal and the valvebody enclose a valve chamber that is not in fluid communication with thespring chamber and the service brake pressure chamber such that fluiddoes not flow from the spring chamber through the valve chamber to theservice brake pressure chamber, wherein the seal is moveable between anopen position in which fluid can flow through the channel between thespring chamber and the service brake pressure chamber and a closedposition in which fluid is blocked from flowing through the channelbetween the spring chamber and the service brake pressure chamber,wherein the seal comprises an opening through which fluid flows when theseal is in the open position, and wherein the opening extends throughthe seal in a direction that is aligned with a direction of movement ofthe seal.
 30. The brake actuator of claim 29, wherein the seal isarranged to move between the open position and the closed position basedon a pressure in the service brake pressure chamber.
 31. The brakeactuator of claim 29, wherein the seal is biased to the open position.32. The brake actuator of claim 31, wherein the seal is arranged to movebetween the open position and the closed position based on a pressure inthe service brake pressure chamber.
 33. A pneumatic brake actuator,comprising: a spring brake actuator comprising a spring chamber and aspring brake pressure chamber; a service brake actuator coupled with thespring brake actuator and comprising a service brake pressure chamber; avalve body that defines a channel between the spring chamber and theservice brake pressure chamber; and a seal positioned within the channelin the valve body, wherein the seal and the valve body enclose a valvechamber that is not in fluid communication with the spring chamber andthe service brake pressure chamber, wherein the seal is moveable betweenan open position in which fluid can flow through the channel between thespring chamber and the service brake pressure chamber and a closedposition in which fluid is blocked from flowing through the channelbetween the spring chamber and the service brake pressure chamber,wherein the seal is biased to the open position, wherein the sealcomprises an opening through which fluid flows when the seal is in theopen position, and wherein the opening extends through the seal in adirection that is aligned with a direction of movement of the seal. 34.The brake actuator of claim 33, wherein the seal is arranged to movebetween the open position and the closed position based on a pressure inthe service brake pressure chamber.
 35. A pneumatic brake actuator,comprising: a spring brake actuator comprising a spring chamber and aspring brake pressure chamber; a service brake actuator coupled with thespring brake actuator and comprising a service brake pressure chamber;an actuator tube comprising a side wall that defines an interior spacewhich is in fluid communication with the spring chamber, wherein theactuator tube comprises a first end positioned adjacent the springchamber and a second end positioned adjacent the service brake pressurechamber, wherein the second end presents an opening; a valve body thatis coupled to the second end of the actuator tube, wherein the valvebody defines a channel that is in fluid communication with the opening;and a seal positioned within the channel in the valve body, wherein theseal and the valve body enclose a valve chamber that is not in fluidcommunication with the spring chamber and the service brake pressurechamber, wherein the seal is moveable between an open position in whichfluid can flow through the channel between the spring chamber and theservice brake pressure chamber and a closed position in which fluid isblocked from flowing through the channel between the spring chamber andthe service brake pressure chamber, and wherein the seal is arranged tomove between the open position and the closed position based on apressure in the service brake pressure chamber.
 36. The brake actuatorof claim 35, wherein the seal is biased to the open position.
 37. Thebrake actuator of claim 35, wherein the valve body is at least partiallypositioned within the interior space of the actuator tube through theopening.
 38. The brake actuator of claim 35, wherein the seal comprisesa first sealing surface that engages the valve body when the seal is inits closed position to prevent fluid from flowing between the springchamber and the service brake pressure chamber, and wherein the sealcomprises second and third sealing surfaces each of which engages thevalve body to seal the valve chamber from the spring chamber and theservice brake pressure chamber.
 39. A pneumatic brake actuator,comprising: a spring brake actuator comprising a spring chamber and aspring brake pressure chamber; a service brake actuator coupled with thespring brake actuator and comprising a service brake pressure chamber; avalve body that defines a channel between the spring chamber and theservice brake pressure chamber; and a seal positioned within the channelin the valve body, wherein the seal and the valve body enclose a valvechamber that is not in fluid communication with the spring chamber andthe service brake pressure chamber, wherein the seal is moveable betweenan open position in which fluid can flow through the channel between thespring chamber and the service brake pressure chamber and a closedposition in which fluid is blocked from flowing through the channelbetween the spring chamber and the service brake pressure chamber,wherein the seal is arranged to move between the open position and theclosed position based on a pressure in the service brake pressurechamber, wherein the seal comprises a first sealing surface that engagesthe valve body when the seal is in its closed position to prevent fluidfrom flowing between the spring chamber and the service brake pressurechamber, and wherein the seal comprises second and third sealingsurfaces each of which engages the valve body to seal the valve chamberfrom the spring chamber and the service brake pressure chamber.
 40. Thebrake actuator of claim 39, wherein the seal comprises an openingthrough which fluid flows when the seal is in the open position, andwherein the opening extends through the seal in a direction that isaligned with a direction of movement of the seal.
 41. The brake actuatorof claim 39, wherein the seal is biased to the open position.